Chemistry. — '' Determination of the Configaration of cis-trans 

 isomeric substances'. By Pi-of. J. Büeseken and Chk. van 



liOON. 



(Communicated in the meeting of May 25, 1918). 



1. The appearance in a number of isomers of unsaturated and 

 cyclic compounds, has undoubtedly been a momentous incitement 

 to the acceptance of van 't Hoff's hypothesis on the carbon atom, 

 which is supposed to lie in the centre of its valencies. 



The permanence of the optical activity at moderate temperatures 

 necessitated the attribution of a rather great stability to these 

 valencies. Obviously in cyclic molecules the same rigidity had to be 

 accei)ted, and also around the double bond. 



Apart from objections that may rise against the substance of this 

 supposition ■ — objections connected with hypotheses on the internal 

 structure of the atom — it must be granted that a very elegant 

 interpretation has been given of the existence of the aforesaid isomers. 



In fact, oidy very seldom cis-trans isomei'ism could not be observed 

 when it was to be expected according to this theory, while on tlie 

 other hand, if identical radicles are united to one of the unsaturated 

 atoms or members of the ring, and therefore no isomers are to be 

 anticipated, they were indeed not to be found. 



2. This interpretation of the existence of cis-trans isomers is 

 little to be doubted ; however, it is much more difïicult to determine 

 which isomer has the cis- and which the trans-configuration. 



By a happy coincidence the classical case of cis-trans isomerism, 

 viz. that of maleic and f u marie acid, has offered, also in this respect, 

 the greatest certainty. 



H— C— COOH HOOC— C-H 



H— C— GOOH H— C— OOOH 



maleic acid fu marie acid 



The cause is evident: the configuration determination here is based 

 almost exclusively on properties that may be deduced from the 

 molecules themvSelves. 



The determination namely of the configuration of geometrical 

 isomers takes place along different lines. 



